It's been interesting, and a little complex. The first time that Haydos issued the call [and surely it's only a matter of time before Mongoose provide him with some sort of pocket-sized Viking horn which he can blow when he wants it brought out], he bludgeoned five fours and seven sixes from the next 34 balls he faced. The second time he pulled it out, for the highly entertaining super over between CSK and Punjab yesterday, he was knocked over first ball, a ball he missed by a spectacular and not undisturbing distance.
First the obvious point. The Mongoose is not aimed at a player like Matthew Hayden, who can clear any boundary on earth with a regular bat and thus need not increase his risk. Until Lalit Modi decides to reward big shots with runs commensurate to the distance hit [oh, it'll happen...], the only value Hayden gained was novelty. The trajectory of his hits seemed slightly shallower, the forward momentum slightly greater, not unlike a punched iron shot in golf. He also selected his moment well, a flat low pitch on a day where pitching short was even more fraught with risk for the bowler. On those terms, it was a marketing stunt, nothing more. Unless you have an eye like Hayden's the bat remains essentially useless, or at least disadvantageous, in a match situation.
In short [and it is short], it's a very IPL bat. And yet a new piece of kit is teaching an old lesson. Hayden's power with the Mongoose came from the batspeed. The long handle helped, but the force of the hit came from the overall lightness of the bat. If the club player is to draw some value from the Mongoose, it's that weight is key. There's no point in having a bat so heavy you can't swing it fast. It's nothing new. As WG said of his first coach, his uncle Pocock, 'he made sure I had a bat to suit my strength'.
What would be truly interesting would be to see Hayden using a full-size blade of around 2lbs 7oz. My guess is he'd hit it as far as the Mongoose. There's another interesting bat about to come onto the market, the Joker. It is more traditional in shape, but with the kind of profile you'd find on John Holmes in tight shorts. It weighs 2lbs 8ozs, and I guess [again] that it is the VHS to the Mongoose's Betamax.
A final thought. If I was captaining against Hayden, I'd have the bowler try and knock his head off, and not bother about him being called for no balls. That'd be controversial, and Lalit would love it, of course...